密度泛函理论研究鸟氨酸盐在Mg(0001)表面的吸附机理

镁及镁合金具有与人体自然骨的密度相近,良好的生物相容性等特点,但作为生物医用材料植入人体之后,及易降解和腐蚀.本论文用密度泛函理论研究了鸟氨酸盐在Mg(0001)表面的吸附,通过吸附能,态密度,电荷差分密度等分析发现鸟氨酸盐在Mg(0001)表面存在强烈的Mg-O和Mg-N相互作用,从而鸟氨酸盐有望在镁金属的表面可以形成一层致密的氧化膜,达到改善镁金属材料的耐腐蚀性,降低降解速度的目的 .     

有机添加剂柠檬酸与乙二胺四乙酸吸附在Mg(0001)表面的计算模拟研究

镁及镁合金具有良好的生物降解性, 生物相容性和优异的力学相容性, 作为新一代理想的可降解医用金属材料具有巨大的潜力, 但植入人体后, 极易腐蚀和降解. 本工作用密度泛函理论计算模拟方法研究了有机添加剂柠檬酸与乙二胺四乙酸在Mg(0001)表面的吸附. 通过吸附能, 分态密度, 差分电荷密度及布居电荷分析发现柠檬酸与乙二胺四乙酸在Mg(0001)表面存在强烈的Mg-O“单齿”和O-Mg-O“双齿”共价相互作用, 而乙二胺四乙酸平躺于Mg(0001)表面有最强的相互作用. 研究结论有望为在有机添加剂改善镁及镁合金生物医用材料的腐蚀及降解方面提供有用的理论指导.     

ZnO(0001)表面吸附B的电子结构和光学性质研究

采用基于密度泛函理论的总体能量平面波超软赝势方法,结合广义梯度近似,对清洁ZnO(0001)表面及B/ZnO(0001)吸附体系进行了几何结构优化,计算了B/ZnO(0001)吸附体系的吸附能、能带结构、电子态密度和光学性质.计算结果表明:B在ZnO(0001)表面最稳定的吸附位置是T₄位.吸附后B/ZnO(0001)吸附体系表面带隙有所减小,表面态的组成发生变化,n型导电特性有一定程度的减弱,同时,对紫外光的吸收能力显著增强. 关键词： ZnO(0001)表面 B吸附 电子结构 光学性质     

ZnO 极性表面及其N原子吸附机理的第一性原理研究

基于密度泛函理论的第一性原理赝势法计算了ZnO极性表面的几何结构和电子结构特性,对比分析了ZnO(0001)和ZnO(0001)表面结构弛豫、能带结构、电子态密度及N吸附ZnO极性表面的形成能情况.计算结果表明: 相对于ZnO(0001)表面,ZnO(0001)表面受结构弛豫影响更加明显,而ZnO(0001)表面完整性更好.相对于体相ZnO结构,ZnO(0001)表面的能带带隙变窄,同时价带顶附近能级非局域性增强使晶体表面的导电性能变得更好;而ZnO(0001)表面的能带带隙变宽,由于O^{-关键词： 密度泛函理论 第一性原理 ZnO极性表面 N吸附}     

Ba和Sr原子在ZnO(0001)表面吸附的密度泛函理论研究

我们采用密度泛函理论下的平面波赝势方法研究Ba和Sr原子在ZnO(0001)表面的吸附结构和性质,仔细研究了三个吸附位（T4, H3 and Top）。发现Ba和Sr吸附在表面的H3和T4位时,他们之间的结合能相差很小,且这两种金属更易于吸附在表面的T4位,我们把计算的结果与贵金属在ZnO(0001)表面的吸附行为及前人的实验结果进行了比较,理论上发现Ag和Au易于吸附在ZnO(0001)表面的H3位,而实验上观察到即使在很小吸附比的条件下ZnO(0001)表面上也能形成Cu的团簇结构,这主要是由于Cu和ZnO(0001)表面衬底强的相互作用所致。     

Ba和Sr原子在ZnO(0001)表面吸附的密度泛函理论研究

我们采用密度泛函理论下的平面波赝势方法研究Ba和Sr原子在ZnO(0001)表面的吸附结构和性质,仔细研究了三个吸附位（T4, H3 and Top）。发现Ba和Sr吸附在表面的H3和T4位时,他们之间的结合能相差很小,且这两种金属更易于吸附在表面的T4位,我们把计算的结果与贵金属在ZnO(0001)表面的吸附行为及前人的实验结果进行了比较,理论上发现Ag和Au易于吸附在ZnO(0001)表面的H3位,而实验上观察到即使在很小吸附比的条件下ZnO(0001)表面上也能形成Cu的团簇结构,这主要是由于Cu和ZnO(0001)表面衬底强的相互作用所致。     

Be(0001)薄膜中的量子尺寸效应与吸附氢的第一性原理计算

通过基于密度泛函理论的第一性原理方法对铍自由表面的电子结构及表面原子氢的吸附能作了详细计算，给出Be(0001)薄膜的电子结构、表面能、电子功函数、层间弛豫等物理量随厚度变化关系，同时讨论了原子氢在Be(0001) 表面的吸附性质，给出了吸附能及局域电子态密度随铍薄膜层厚的变化关系，体现了铍薄膜的量子尺寸效应.     

Ba和Sr原子在ZnO(0001)表面吸附的密度泛函理论研究（英文）

我们采用密度泛函理论下的平面波赝势方法研究Ba和Sr原子在ZnO(0001)表面的吸附结构和性质,仔细研究了三个吸附位(T_4,H_3和Top).发现Ba和Sr吸附在表面的H3和T4位时,他们之间的结合能相差很小,且这两种金属更易于吸附在表面的T_4位,我们把计算的结果与贵金属在ZnO(0001)表面的吸附行为及前人的实验结果进行了比较,理论上发现Ag和Au易于吸附在ZnO(0001)表面的H3位,而实验上观察到即使在很小吸附比的条件下ZnO(0001)表面上也能形成Cu的团簇结构,这主要是由于Cu和ZnO(0001)表面衬底强的相互作用所致.     

Cs/GaN(0001)吸附体系电子结构和光学性质研究

采用基于第一性原理的密度泛函理论平面波超软赝势方法计算了 1/4ML Cs原子吸附 (2 × 2) GaN(0001) 表面的吸附能、能带结构、电子态密度、电荷布居数、功函数和光学性质. 计算发现, 1/4ML Cs 原子在 GaN(0001) 表面最稳定吸附位为 N 桥位, 吸附后表面仍呈现为金属导电特性, Cs原子吸附GaN(0001)表面后主要与表面 Ga 原子发生作用, Cs6s 态电子向最表面 Ga 原子转移, 引起表面功函数下降. 研究光学性质发现, Cs 原子吸附 GaN(0001) 表面后, 介电函数虚部、吸收谱、反射谱向低能方向移动.     

单原子Pt增强α-Mo_2C(0001)抗硫中毒特性机理的第一性原理研究

采用基于密度泛函理论(DFT)第一性原理方法研究了α-Mo_2C(0001)表面和Pt/α-Mo_2C(0001)表面抗硫中毒特性及其机理.发现干净的Mo_2C(0001)表面对含硫物种(S、HS和H2S)吸附很强(吸附能分别为-6.46、-4.15和-1.54 e V),极易S中毒.Pt的引入可以减弱含硫物种在Mo_2C(0001)表面的吸附,当含硫物种在Pt/Mo_2C(0001)表面Pt原子周围吸附时吸附能较小,在Pt原子顶位吸附时吸附能最小,远离Pt原子吸附时吸附能增大.因此,Pt的引入对Pt周围催化活性位点避免硫原子中毒起到很好的保护作用,达到抗硫中毒效果.预期提高Pt原子覆盖度,可以进一步降低含硫物种与Mo_2C(0001)表面的相互作用,更好地抗硫中毒,为设计高活性、高抗硫中毒性的Mo_2C基催化剂提供理论依据.     

Influences of Al doping on the electronic structure of Mg(0001) and dissociation properties of H2

By using the density functional theory method, we systematically study the effects of the doping of an Al atom on the electronic structures of the Mg(0001) surface and on the dissociation behaviors of H₂ molecules. We find that for the Al-doped surfaces, the surface relaxation around the doping layer changes from expansion of a clean Mg(0001) surface to contraction, due to the redistribution of electrons. After doping, the work function is enlarged, and the electronic states around the Fermi energy have a major distribution around the doping layer. For the dissociation of H₂ molecules, we find that the energy barrier is enlarged for the doped surfaces. In particular, when the Al atom is doped at the first layer, the energy barrier is enlarged by 0.30 eV. For different doping lengths, however, the dissociation energy barrier decreases slowly to the value on a clean Mg(0001) surface when the doping layer is far away from the top surface. Our results well describe the electronic changes after Al doping for the Mg(0001) surface, and reveal some possible mechanisms for improving the resistance to corrosion of the Mg(0001) surface by doping of Al atoms.     

Comparative study of adsorption characteristics of Cs on the GaN （0001） and GaN （0001） surfaces

The adsorption characteristics of Cs on GaN （0001） and GaN （0001） surfaces with a coverage from 1/4 to 1 monolayer have been investigated using the density functional theory with a plane-wave uttrasoft pseudopotential method based on first-principles calculations. The results show that the most stable position of the Cs adatom on the GaN （0001） surface is at the N-bridge site for 1/4 monolayer coverage. As the coverage of Cs atoms at the N-bridge site is increased, the adsorption energy reduces. As the Cs atoms achieve saturation, the adsorption is no longer stable when the coverage is 3/4 monolayer. The work function achieves its minimum value when the Cs adatom coverage is 2/4 monolayer, and then rises with Cs atomic coverage. The most stable position of Cs adatoms on the GaN （000i） surface is at H3 site for 1/4 monolayer coverage. As the Cs atomic coverage at H3 site is increased, the adsorption energy reduces, and the adsorption is still stable when the Cs adatom coverage is 1 monolayer. The work function reduces persistently, and does not rise with the increase of Cs coverage.     

交换关联泛函近似方法对Ru催化剂上甲烷和乙烷形成的影响

密度泛函理论作为多相催化研究中的一个强有力工具,常被用于获得催化过程中关键的热力学及动力学参数,如吸附能、反应焓、活化能垒和速率常数等. 理解密度泛函交换关联近似方法对于揭示催化剂的催化性能及机理至关重要. 本文报道了六种不同的交换关联泛函近似方法,包括PBE、RPBE、BEEF+vdW、optB86b+vdW、SCAN和SCAN+rVV10,对金属Ru(0001)和Ru(1011)表面上甲烷和乙烷形成过程中涉及到的中间体的吸附能、反应能和活化能垒的影响. 当基元反应中反应物和产物与表面的配位数不同时,理论计算的反应能大小强烈依赖于交换关联密度泛函的选择. 对于涉及多个基元步骤的总反应,反应能的计算偏差会逐渐累积,从而导致不同的交换关联泛函近似方法之间的巨大差异. 由于不同泛函对反应涉及到的中间体吸附能之间存在差异,交换关联泛函近似方法的选择显著地影响Ru(0001)表面上甲烷、乙烯和乙烷的选择性. 然而,不同泛函近似方法对于Ru(0001) 和Ru(1011)表面上基元反应的能垒以及结构敏感性影响不大. 本工作不仅揭示了交换关联密度泛函近似方法在理论计算研究催化领域的局限性,也强调了选择合适的交换关联泛函方法对于正确评估催化剂活性和选择性的重要性.     

Liénard-type chemical oscillator

Using first-principles calculation, we have studied the properties of a series of M _x Co_1?x /Co(0001) (M = Pd, Pt) bimetallic surface alloys with atom M ratios from 0.25 to 1.0, then the effect of alloyed M metal on the properties of S adsorbed on these surfaces are discussed. Our calculations show that the alloying of metal Pd, Pt on Co(0001) weakens the S-M (M = Pd, Pt, Co) bond strength compared to monometallic surfaces and the site preference of sulfur atom is dependent on the alloyed metal M and its surface concentration. Moreover, bimetallic surface electronic structure modifications with and without sulfur are analyzed in comparison with clean Co(0001), and the correlation between the sulfur adsorption energy and the bimetallic surface d-band center is presented.     

Pd对O吸附在ZnO（0001）面上的影响的第一性原理研究

本文用第一性原理方法计算了Pd 在ZnO(0001)面上的吸附、Pd对O吸附的影响及Pd替代表面Zn原子能量的变化.结果表明：(1) Pd的吸附位置不随覆盖度变化,Pd稳定吸附位为H3位;(2)Pd在1/4单层吸附时比1个单层吸附时稳定;(3)Pd的存在增强了氧在ZnO(0001)面上的吸附,O原子可以扩散到Pd吸附层的下,Pd处于最上面, 具有催化作用.     

Adsorption of Xe atoms on metal surfaces: new insights from first-principles calculations

The adsorption of rare gases on metal surfaces serves as the paradigm of weak adsorption where it is typically assumed that the adsorbate occupies maximally coordinated hollow sites. Density-functional theory calculations using the full-potential linearized augmented plane wave method for Xe adatoms on Mg(0001), Al(111), Ti(0001), Cu(111), Pd(111), and Pt(111), show, however, that Xe prefers low coordination on-top sites in all cases. We identify the importance of polarization and a site-dependent Pauli repulsion in actuating the site preference and the principle nature of the rare-gas atom-metal surface interaction.     

A density functional theory study of H2S decomposition on the (1 1 1) surfaces of model Pd-alloys

In this work, we report density functional theory calculations exploring H₂S dissociation on the (1 1 1) surfaces of Pd, Cu, Ag, Au, and various bimetallic surfaces consisting of those metals. To understand the contributions of lattice strain and electronic ligand effects, the thermodynamics of each elementary dissociation step were explored on model bimetallic surfaces, including PdMPd sandwiches and Pd pseudomorphic overlayers, as well as strained Pd(1 1 1) surfaces and homogeneous Pd₃M alloys. Sulfuric (H₂S, SH, and S) adsorption energies were found to correlate very well with lattice constant, which can be explained by the strong correlation of the lattice constant with d-band center, Fermi energy, and density of states at the Fermi level for strained Pd(1 1 1) surfaces. Compressing the Pd lattice shifts the d-band center away from the Fermi level, lowers the Fermi energy, and reduces the density of d-states at the Fermi level. All three effects likely contribute to the destabilization of sulfuric adsorption on Pd alloys. Introducing ligand effects was found to alter the distribution of the d-states and shift the Fermi level, which eliminates the correlation of the d-band center with the density of states at the Fermi level and the Fermi energy. As a result, the d-band center by itself is a poor metric of the H₂S reaction energetics for bimetallic surfaces. Furthermore, combining strain with ligand effects was found to lead to unpredictable alterations of the d-band. Therefore, adsorption of H₂S, SH, and S on PdMPd surfaces do not accurately predict adsorption on Pd₃M surfaces.